Electrode for electron-discharge devices



Sept. 25, 1934. D. A. BARNETT ELECTRODE FOR ELECTRON DISCHARGE DEVICES Filed Jan. '7. 1931 INVENTQR flaw Bar/26 BY A-FI'ORNEY Patented Sept. 25, 1934 UNITED STATES PATENT OEFEQE David A. Barnett, Hamden, Conn assignor, by mesne assignments, to Radio Research Laboratories, Inc., a corporation of Delaware Application January 7, 1931, Serial No. 507,133

' 9 Claims. (01. 250 -275) This invention relates to improvementsiin electrodes for electron discharge devices and more particularly relates to a combined heater and electron emissive cathode element for electron discharge tubes such as rectifier tubes, radio tubes and the. like.

The object of the invention is the provision of such an electrode for a rectifier tube that shall be directly operative on the usual house lighting circuit without the interposition of transformers or voltage-reduction devices.

Another object to the same end is the production of a rectifier tube which is equally effective and non-destructible even when used directlyon the usual housev lighting service, whether it be alternating or direct current.

Another object to the same end isthe production of an essentially, electron emissive cathode, which is included in the heater electrical circuit, especially devised and given enlarged carrying capacityto carry safely not only the current of the heater element but also the full space current of the tube. I I

The present rectifier tubes of the vacuum type are usually constructed with a cathode element heated either directly or indirectly by low voltage secured from astep down transformer, the filament or heating element taking considerable current. In tubes of this type, when inoperation, the rectified or space current is often substantially equivalent to the heating current, thereby injuriouslyincreasing-the current through the filament and appreciably raising its temperature especially toward the negative terminal. This space current is sometimes sufiicient to maintain the. filament temperature when the heating circuit is disconnected so that when both are; acting together, as is usually the case, the filament is operatedat a higher temperature than it should be, thereby tending materially to shorten its life andefficiency;

In the caseof any electron discharge device, such as a radio tube, another object'of the invention is to makethe A circuit offthe tube directly operative from direct current house lighting means or directly from the B current source, whatever it may be, such as a power-pack and the alternating current lighting mains without the necessary interposition of any step down transformer orother voltage-reduction device, the current consumption of such a tube being of the order of a few milliamperes because of the high resistance of the heater.

Another object in the case of any kind of electron discharge device is a combined heater and cathode element operative with a comparatively low cathode temperature and with the heater element subjected to only a fraction of its possible operating voltage, so that it will stand severe over-, loads without being seriously affected thereby.

In short, the novel construction permits the electron discharge device to be used directly at the usual house lighting voltage without the inter-, position of any transformer or voltage-limiting device and is equally applicable for use on alternating or direct current. If used on alternating current, it performs the functions of a rectifier as designed, but if a rectifier tube embodying the invention be inadvertentlyconnected to a direct current house lighting circuit, the tube will merely function as a valve and while in this case it is unnecessary, such misuse of the tube cannot do any damage which would be the case if the tube embodied the usual low voltage filament and other essential alternating current characteristics requiring the use of astep down transformer. v

The accompanying drawing shows only two of the 'difierent ways in which my invention may be embodied, these being put forward as preferred illustrative embodiments of the invention but, of course,without limiting the invention to the details thereof except as same may be important and may be required by the appended claims.

In said drawing, Fig. l is an enlarged perspective view of'one form of combined heater-cathode element or electrode within my invention, this figure also showing broken away the surrounding plate element; Fig. 2is a similarly constituted view of a modified form of combined heater-cathode element within the invention, together with a broken away surrounding plate element; Fig. 3 is an enlarged view of a broken away fragment of the heater-cathode element of Fig. 1; and Fig. 4 is the same as Fig. 3 but with a slightly different cathode construction. Either Fig. 3 or Fig. 4 is also adaptable to the heater construction of Fig. 2.

In Fig. 1, 1 represents a heater-coil of fine wire closely spaced and having the terminal ends 2 and 3. This coil is covered and filled between turns with an electrically insulating coating 4 "around which is wrapped a comparatively heavy conductor 5 preferably in ribbon form, to constitute a return winding to a terminal 13. This heavy conductor 5 is electrically separated from v the heater coil 1 by the intervening insulation. One terminal 3 of the heating coil is united to one end 10 of the heavy conductor 5 whereby said heavy conductor or ribbon forms a continuation of the-heating coil and is part of the circuit of the heating coil current without being substantially affected in producing heat to raise its own temperature, this being produced by the heating coil.

Surrounding the cylindrical insulating coating 4 and contacting with. the ribbon conductor 5 in each turn as at 7 is a moderately large number of turns of small wire 6 which forms the collecting cathode surface of the space current to the plate. The free end 13 of the ribbon conductor surface is both filament and cathode terminal; in other words, the combined heater coil and cathode have only two terminals 2 and 13 for connection with two lead-in wires of the exhausted envelope in which the elements are operatively mounted for connection with the energizing source.

The heater and cathode assembly as described is surrounded by a plate 12 with terminal 21 for connection With the third lead wire through the envelope in the case of a rectifier tube. This plate element 12 may have either a mesh or sheet construction and will otherwise be designed to perform' the usual anode functions. When the inventionis applied to the radio tube or the like having a grid for the control elements, same will be supplied and mounted in well known way in connection with the foregoing elements with appropriate lead connections to the outside of the envelope or tube.

Fig. 3 shows an enlarged fragment of the combined heater-cathode element of Fig. 1 in order to show to better advantage the long, fine wire high resistance winding 1, the insulating shell 4, the ribbon conductor 5, the auxiliary winding 6 and the emissive coating 8 which is sprayed or painted over the outside of the auxiliary winding 6, the ribbon conductor 5 and the insulating shell 4.

Thus, the aforesaid typical embodiment of the invention comprises a close spaced coil of very fine wire wound on a suitable mandrel with an insulating material covering the outside of said coil and filling the interstices between the. turns of the winding both for insulation andsupport, said winding being continued at one end of the outside of the insulating coating as a return winding of comparatively few turns and comparatively large cross section, preferably in ribbon form, the latter being afterwards coated with a suitable electron emissive material so as to constitute said ribbon the essential electron emissive portion of the entire electrode.

In Fig. 2 showing the second illustrative embodiment of the invention, 14 isa hollow cylinder of electrically insulating refractory material having a plurality of longitudinal holes or bores 15 in which are successively threaded or looped a fine wire heating coil 16 having a starting terminal 17 adapted to be connected to one pole of the energizing source and having an ending terminal 18 connected to one end of the oathode ribbon 19 which in turn ends as terminal 20 for connection with the other pole of the energizing source to constitute the cathode of the combined heater-cathode element. 6 is the fine Wire auxiliary winding of the same nature as described in Fig. 1.

Fig. 4 is an enlarged fragmentary view of the heater-cathode element of Fig. 1 except for the modification that the ribbon cathode 9 is wound in a close spiral so as to cover practically the entire surface of the insulating covering and thereby do away with the necessity of the auxiliary winding of fine wire 6 as a current'collector.

As before, this ribbon cathode 9 is of such relatively large cross section as compared to the wire of the heating coil 16 of which it is a continuation to complete the heating circuit, that the very small heating current due to the high resistance of the heating coil is not effective to raise appreciably the temperature of the ribbon cathode. The low relative resistance and short 'length of the ribbon cathode 9 take up only a negligible percentage of the fully applied line or other B source voltage so that the difierence of potential between the two ends of the ribbon current to produce a comparatively low heat ef- I" fect, one end of the entire heating element being continued in a large cross-sectioned short length return winding about the outside of the insula ing cylinder as previously described.

The large cross-section of the cathode end of the filament in either of the embodiments (Figs. 1 or 2) may consist of as little as one turn, its outer surface being then covered with the described moderately close spaced auxiliary winding of fine wire, each turn of which makes oontact with the enlarged or ribbon-like "cathode whereby said ribbon acts only as a contacting medium for the plate or space current in which case a fine wire auxiliary winding is the collecting surface. said embodiments, Fig. 1 or 2, may have the cathode end of the heating coil consist of a thin ribbon wound in a number of turns about the refractory insulation separating it from the heating coil, said turns being slightly spaced from each other so as to substantially cover the entire outside surface of the insulation. In any case, the emissive compound of any suitable preferred nature is sprayed or coated over the cathode and the fine wire collecting surface.

The effect of either single turn heavy conductor with fine wire collecting surface, or the substantially covered surface with ribbon conductor, is to make effective as a cathode approximately the entire outer surface with a negligible potential gradient between the two ends of the cathode and the anode.

What I claim is:

1. An electrode for an electron discharge tube which comprises a fine wire heating element; and a ribbon-like electron emissive cathode in series with said fine wire heating element which it surrounds out of short-circuiting contact therewith, and means for short-circuiting the turns of said ribbon-like cathode to enable it to carry not only the heating current of the heating element but also a large space current in addition.

2. An electrode for an electron discharge tube which comprises a coiled fine wire high resistance heating element; and a ribbon-like electron emissive cathode in series with said coiled heating element, about which it is wrapped spirally out of short-circuiting contact therewith, and means for short-circuiting only the turns of said ribbonlike cathode.

As another alternative, either of it 3. An electrode for an electron discharge tube which comprises a coiled fine wire high resistance heating element; a hollow cylindrical support of electrically insulating material upon the interior face of which said coiled heating element is supported; and a ribbon-like electron emissive cathode in series with said heating element wrapped spirally about said insulating support.

l. An electrode for an electron discharge tube which comprises a coiled fine wire high resistance heating element; a support of electrically insulating material surrounding said coiled heating element; a ribbon-like cathode in series with said heating element wrapped spirally about the insulating support; and a layer of wire wrapped about said support and said ribbon-like cathode with the latter short-circuiting the turns of said wrapping wire.

5. An electrode for an electron discharge tube which comprises a coiled fine wire high resistance heating element; a support of electrically insulating material surrounding said coiled heating element; a ribbon-like cathode in series with said heating element wrapped spirally about the insulating support; a layer of wire wrapped about said support and said ribbon-like cathode with the latter short-circuiting the turns of said wrapping wire; and material applied to said cathode and wrapping Wire which is electron emissive at low temperatures.

6. A rectifier tube which comprises a high vacuum envelope, and an anode, a wound cathode and a heating element for said cathode operatively supported in said container, said cathode being a continuation of and surrounding said heating element in closed spaced but insulated relation thereto, said heating element, and cathode forming a series electrical circuit operated at voltages as high as house lighting voltages, the turns of said cathode being spaced apart from each other, whereby the current flowing through the heating element also flows through said cathode to aid in heating the said cathode.

'7. A rectifier tube which comprises a high resistance small cross-sectional heating element,

a wound cathode of low resistance and relatively large cross-section surrounding and insulated from said heating element, said cathode being a continuation electrically of said heating element, the combined heating and cathode elements being operative at voltages as high as house lighting voltages; an anode surrounding said cathode; a highly evacuated container operatively supporting said elements, said heating and cathode elements together being connected to two terminals of said container and the anode being connected to a third terminal, the turns of said cathode being spaced apart from each other, whereby the current flowing through the heating element also flows through said cathode to aid in heating the said cathode.

8. An electrode for an electron discharge tube which comprises a high resistance heating element and a wound cathode, said cathode closely surrounding said heating element out of short circuiting contact therewith, said heating coil and said cathode being series-connected and having a sufliciently high combined resistance for direct operation at voltages as high as lighting voltages, said cathode being constituted as compared to the heating coil so that the electron emission is essentially from the cathode, and with its turns spaced apart from each other, whereby the current flowing through said cathode to aid in heating the said cathode.

9. An electron discharge device comprising an anode, a long fine filamentary heating element, and a ribbon-like cathode spirally wrapped about said filamentary heating element but out of shortcircuiting contact therewith, said heating element and cathode being series connected and having a voltage-current characteristic enabling the cathode to be brought to emitting temperature with current through said heater of the order of the normal anode current of the device, the turns of said cathode being spaced apart from each other, whereby the current flowing through the heating element also flows through said cathode to aid in heating the said cathode.

DAVID A. BARNETT. 

